title: Holmium:YAG percutaneous nephrolithotomy: the laser incident angle matters.
abstract: OBJECTIVE
  Laser physics dictate that maximal radiant exposure occurs when the laser strikes the target at a normal incidence. Since the renal collecting system often limits nephroscope movements during percutaneous nephrolithotomy, the laser-calculus incidence angle may vary. We have observed during holmium:YAG percutaneous nephrolithotomy that the side firing fiber more easily approaches a normal incidence compared to the end firing fiber. We test the hypothesis that holmium:YAG percutaneous nephrolithotomy is faster with a side firing fiber compared to an end firing fiber.
  
  
  METHODS
  Consecutive holmium:YAG percutaneous nephrolithotomy cases were studied retrospectively. The calculus size and composition, surgical time, fragmentation speed (size/time) and stone-free rates were compared between 11 patients treated with end and 8 treated with side firing fibers.
  
  
  RESULTS
  When the end and side firing groups were compared, calculus sizes (mean plus or minus standard deviation) were 22 +/- 13 versus 48 +/- 17 mm. (p = 0.004), calcium oxalate monohydrate incidence was 55 versus 75% (p = 0.3), surgical times were 168 +/- 87 versus 124 +/- 51 minutes, computed fragmentation speeds were 0.15 +/- 0.09 versus 0.43 +/- 0.15 mm. per minute (p = 0.0009) and stone-free rates were 73 versus 88% (p = 0.4), respectively.
  
  
  CONCLUSIONS
  The side firing fiber is faster than the end firing fiber for holmium:YAG percutaneous nephrolithotomy. These results are consistent with principles of laser physics.
authors.affiliation: Division of Urology, University of Texas Health Science Center San Antonio 78284-7845, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Teichman
authors.forename: R D
authors.initials: RD
authors.lastname: Rao
authors.forename: R D
authors.initials: RD
authors.lastname: Glickman
authors.forename: J M
authors.initials: JM
authors.lastname: Harris
mesh_terms: D000535:Aluminum; D055592:Biophysical Phenomena; D001703:Biophysics; D006695:Holmium; D006801:Humans; D007669:Kidney Calculi / Q000628:therapy*; D007834:Lasers; D017602:Lithotripsy, Laser; D009403:Nephrostomy, Percutaneous / Q000379:methods*; D012189:Retrospective Studies; D016896:Treatment Outcome; D015019:Yttrium
chemical_list: D015019:Yttrium; D000535:Aluminum; D006695:Holmium